Photosynthetic reaction centers from bacteria are incorporated into planar and large vesicular membranes. In such membranes, the kinetic and steady state aspects of the electron flow generated by steady light and single turnover laser flashes are analysed through direct measurements of the electric currents and potentials, and compared with theoretical predictions based on model calculations. Externally applied potentials, replacement of the endogeneous ubiquinones by other quinones of known redox potentials, variations of the electron donor and acceptor in the aqueous phase and modification of the membrane lipids serve as additional tools for the analysis. Cyclic electron transport is reconstituted by the incorporation of reaction centers and mitochondrial b-c1 complex in to the same membrane. Densely packed monolayers of reaction centers are sandwiched between two transparent metal electrodes. Photo-induced currents and potentials generated in these devices are studied at normal and liquid helium temperatures and correlated with optical measurements. Cytochrome oxidase is incorporated into planar bilayers separating two aqueous phases. The kinetic and steady state aspects of transmembrane electron currents and potentials generated in these membranes through oxidation of reduced cytochrome c are measured by voltage and current clamp techniques. The absorption spectra of the electron transport proteins within the membrane are measured by attenuated total internal reflection of light entering the membrane parallel to its plane through a transparent support. Spectra are correlated with the membrane potential, redox state of the electron transport components and the pH. Methods are developed for the formation of planar crystals of reaction centers which are then used for structural analysis by diffraction and image reconstruction methods. It is expected that these studies will give new insights into the molecular mechanisms of vectorial charge separation across biological membranes involved in photosynthesis and metabolism.